Wrong boiler starts

[Dainiux]

Hello, can't understand the reason, why boiler heating starts a night. It started week ago. I have RC35 set schedule - daytime heating (HC1) start at 5:30 until 21:30. Now we have warm weather and heating at night is not necessary. But by unknown reasons now I see, that every night heating starts randomly at 00:30 - 1:30 and works on maximum heating temperature until daytime mode starts - and heating temperature drops to normal (as I understand, circulation pomp does not works during these night starts therefore boiler reach max temperature 75C). Reset does not helps. Where to dig?